Nuclear battery

ABSTRACT

Nuclear battery including one or more cells each comprising a radioactive fuel element or source and a semiconductor element positioned contiguously to the source and irradiated by it. The fuel element includes a radioactive material which is preferably promethium-147 metal or its oxide, promethia, and the semiconductor element includes a N /P or N /P/P semiconductor wafer which is preferably silicon. The semiconductor wafer has an energy threshold of radiation damage which is compatible with the maximum energy of the nuclear particles or radiation emitted by the radioactive material, to provide a long-life (minimal radiation damage) cell of optimum power output. Other versions include a nuclear battery utilizing a bi-directional fuel element, and certain compact and useful embodiments utilizing a multiple section cell therein.

United States Patent Olsen et a1. 1451 Dec. 19, 1972 1541 NUCLEARBATTERY Primary Examiner-Rodney D. Bennett, Jr. [72] Inventors: Larry C.Olsen, Richland; Stephen Asmtam Exammer *1 M Potenzia E. Seeman,Kennewick; Bobby I. Griffin; Charles J. Ambrose, both of Attorney-WalterJ. Jason, Donald L. Royer and D. N. Jeu

[5 7 ABSTRACT Nuclear battery including one or more cells eachcomprising a radioactive fuel element or source and a semiconductorelement positioned contiguously to the source and irradiated by it. Thefuel element includes a radioactive material which is preferablypromethium-147 metal or its. oxide, promethia, and the W,

semiconductor element includes a N /P or N ll 'll semiconductor waferwhich is preferably silicon.

12 Claims, 24 Drawing Figures V y} 52' 4% V/\\ fl NUCLEAR BATTERYBACKGROUND OF THE INVENTION Our present invention pertains generally tothe field of batteries and more particularly to a nuclear batterywherein nuclear energy is usefully converted into electrical energy.

Generally, prior radioactive or nuclear batteries which involve theconcept of coupling a radioactive source with one or more semiconductorelements have utilized a source of high energy radiation to irradiatethe semiconductor elements that each include a NP junction therein. Theradiation damage created by the high energy particles or radiation inthese prior batteries is so great, however, that their useful lifetimesare so short as to render such batteries to be of questionable value.

Further, the power density, maximum output power, maximum output voltageand device efficiencies are relatively quite low for the priorradioactive or nuclear batteries. The various known concepts ofradioactive or nuclear batteries do not in most instances appear to beparticularly feasible, and all of such concepts are either clearlyimpractical or are of little useful value. It is, of course, well knownthat a general purpose nuclear battery other than this invention and ofa similar category is not presently and readily available on thecommercial market.

SUMMARY OF THE INVENTION Briefly, and in general terms, our invention ispreferably accomplished by providing a nuclear battery including one ormore cells each comprising a radioactive fuel element or source and asemiconductor element positioned in close proximity or contiguously tothe source and irradiated by it.

The semiconductor element is made of a material which has an energythreshold level of radiation damage that is compatible with the maximumenergy of the nuclear particles or radiation emitted by the radioactivesource. The fuel element includes a radioactive material which ispreferably promethium- 147 (Pm") metal or its oxide, promethia Pm,o, andthe semiconductor element includes a N /P or N /P/P semiconductor waferwhich is preferably silicon (Si), to provide a long-life (minimalradiation damage) cell of optimum power output. The semiconductor waferis preferably characterized by having at least a N*-type layer which hasa very high density of conduction electrons. In the three-layersemiconductor wafer, the I- type layer has a very high density ofholes," of course. In both instances (N? or I), the carrier densitypreferably approaches or 10 carriers/cm in order that maximum voltage beobtained.

The radioactive fuel element and the semiconductor element of a cell arepreferably discs of similar sizes. The fuel element is also preferablypositioned virtually against the N -type layer surface of thesemiconductor wafer. The N"/l and NVlP/ll (silicon) semiconductor wafersare preferred because they are more resistant to damage caused by (beta)radiation. However, PIN and WIN/N semiconductors (N-type semiconductorstock) can, of course, be used satisfactorily in this invention.

In the NH]? semiconductor wafer, the highly doped N -type layer facethereof provides a large number of conduction electrons which areavailable to an external circuit or load. In the N IPIP semiconductorwafer, both faces thereof are highly doped to have high carrierconcentrations such that the resulting N*-type layer and P*-type layerfaces prevent any bending of the electron bands in the wrong sense andthus generate an electromotive force of the incorrect polarity. Thesehighly doped surfaces essentially lock" the electron bands in placewhereby the semiconductor surfaces can be treated in any manner desiredwithout degrading device performance. In such an arrangement, ohmiccontacts can be easily made to the semiconductor faces and, in fact, anyadjacent oxide layers formed thereon will not alter the electron bandstructure to affect the performance of the device. The resulting nuclearbatteries can be manufactured with power levels covering a wide rangeand have long lifetimes (of over three years) with high power densities(of one milliwatt/cm or more).

Other versions of our invention include a two-cell nuclear batteryutilizing a bi-directional fuel element or source, a planar multiplesection cell nuclear battery embodiment, a laminar multiple section cellnuclear battery configuration and an elongated, cylindrical multiplesection cell nuclear battery embodiment. The nuclear batteryconfigurations including a multiple section cell therein areparticularly compact and practical forms of our invention, and cansupply electrical power at voltages much greater than that availablefrom an equivalent single cell which utilizes only one active area.

BRIEF DESCRIPTION OF THE DRAWINGS Our invention will be more fullyunderstood, and other features and advantages thereof will becomeapparent, from the following description of certain illustrativeembodiments of the invention. The description is to be taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a central sectional and elevational view, perspectively shown,of a nuclear battery constructed in accordance with our invention;

FIGS. 2A and 2B are enlarged fragmentary and central sectional views ofa fuel element and its concentric ring, and a semiconductor element,respectively, of the nuclear battery shown in FIG. 1;

FIG. 3 is an enlarged fragmentary and central sectional view of adirectly fueled nuclear battery cell;

FIG. 4 is an electron energy level diagram for a NVP/P semiconductordevice;

FIG. 5 is a circuit diagram showing a resistive load connected topositive and negative electrodes of a N /P semiconductor device;

FIG. 6 is a circuit diagram of an equivalent circuit of thesemiconductor device shown in FIG. 5 connected to its resistive load;

FIG. 7 is a graph illustrating current density and power density versusoutput voltage characteristics of a single cell device constructedaccording to this invention;

FIGS. 8A, 8B, 8C and 8D are graphs which were plotted from experimentalresults and show typical characteristics of promethia-fueled, siliconsemiconductor, betavoltaic single cells as a function of promethia layerthickness;

l060ll 0590 FIGS. 9A and 9B are respectively a perspective view of abi-directional fuel element or source, and a fragmentary and enlargedsectional view thereof;

FIGS. 10A and 10B are exploded perspective views of atwo-cellbetavoltaic energy converter or battery using the bi-directionalsource of FIG. 9A, wherein the cells are connected respectively inparallel and in series;

FIG. 11 is an elevational view of a N /P semiconductor wafer having apromethium coating deposited directly onto the N -type layer surface ofthe wafer;

FIG. 12 is an exploded perspective view of a two-cell betavoltaicbattery having a radioactive material coated directly on at least onesemiconductor wafer of the cells;

FIG. 13 is an exploded perspective view of a highly compact andpractical form of a nuclear battery constructed according to thisinvention;

FIG. 14 is'a graph illustrating the current and power versus voltagecharacteristics of a nuclear battery such as that shown in FIG. 13;

FIG. 15 is an exploded perspective view of a planar, multiple section,cell embodiment of a nuclear battery;

FIG. 16 is a partially fragmentary and exploded perspective view of alaminar, multiple section, cell configuration of a nuclear battery;

FIG. 17 is an electron energy level diagram for about two sections ofthe N /P /P semiconductor device shown in FIG. 15; and

FIG. 18 is an exploded and partly fragmentary perspective view of anelongated cylindrical, multiple section, cell embodiment of a nuclearbattery.

DESCRIPTION OF THE PRESENT EMBODIMENTS FIG. I is a central sectional andelevational view, perspectively shown, of a nuclear battery 30constructed in accordance with our invention. The battery 30 broadlyincludes a radioactive fuel-semiconductor stack 32, and inner and outercontainers 34 and 36 for suitably enclosing and housing the stack. Thestack 32 includes lower and upper metallic discs 38 and 40 whichsandwich a number of radioactive fuel elements 42 and semiconductorelements 44 that are contiguously positioned in alternate layers. Thediameter of the fuel elements 42 is smaller than that of thesemiconductor elements 44, such that metallic rings 46 having an innerdiameter larger than that of the fuel elements and an outer diameterequal to that of the semiconductor elements, can be positionedconcentrically around and radially spaced from the semiconductorelements in the same corresponding layers thereof.

The lower metallic disc 38 is in direct contact with the lower fuelelement 42 and its concentric metallic ring Q6. The upper metallic disc&0 is in direct contact with the upper semiconductor element 44. Aninsulating liner 48 made of radiation resistant rubber or an oxide, forexample, is provided'around the sides or circumferential surface of thestack 32 and over the upper surface of the metallic disc 60 except for acentral area 40a thereof, as shown in FIG. 1. The liner 45 insulates thestack 32 from the inner sleeve 34a of inner container 34 which can befabricated of tantalum (Ta), for example. The inner container 3tincludes an outer sleeve 34b which is closed at its lower end to supportthe stack 32 through a metallic spring ring 50. The

spring ring 50 also provides an electrical connection between the lowerdisc 38 and the inner container 34.

The inner container 34 is enclosed by and in direct. contact with theouter container 36 which is preferably a closed stainless steel firecan. The outer container 36 includes a lower can portion 36a and anupper cover portion 36b which can be electron beam welded to the canportion at the juncture 52 thereof. The cover portion 36b has a centraland countersunk hole 54 therein. A small insulating sleeve 56 of ceramicor glass, for example, is positioned within the countersunk portion ofthe hole 54 and supports a closing metallic disc'58 which iselectrically connected by lead 60 to the central area 40a of the uppermetallic disc 40. Glass-to-metal seals are, of course, suitably providedat the lower and upper ends of the insulating sleeve 56. Thus, the disc58 is one (positive) electrode andthe outer container 36 is the other(negative) electrode of the nuclear battery 30. The battery 30 as shownillustratively in FIG. l is cylindrical in configuration; however, itobviously can be made in rectangularor other configurations. The battery30 has outside or overall dimensions of diameter D and length L.

FIGS. 2A and 2B are enlarged fragmentary and central sectional views ofa fuel element 42 and its concentric ring 46, and a semiconductorelement 34, respectively. In FIG. 2A, the ring 46 can be made ofaluminum (Al) and can have an outer diameter of approximately 1 cm, forexample. The fuel element 42 includes an aluminum disc 42a and a thinlayer 4212 of promethia (Pm O thereon. The ring so can have an innerdiameter of approximately 0.95 cm, and the disc 42a can have a diameterof approximately 0.93 cm and a thickness typically of from 3 to 10 mils.This thickness is primarily for strength andhandling. Nickel (Ni) ortantalum, for example, can be used instead of aluminum. The disc 42a ispreferably sand-blasted on a face first and then the promethia layer 42bcan be provided tenaciously thereon by vapor deposition. The promethialayer 42b can be provided on the face with a layer thickness ofapproximately 5.3 milligram/cm for example. Promethia is preferably usedsince it is a good and stable source ofbeta particles or radiation. Itis, of course, to be understood that the various types of materials. anddifferent dimensions noted herein are given by way of example only andare not intended to be restrictive or limiting on the scope of ourinvention in any manner.

In FIG. 2B, the semiconductor element 414 has an outer diameter which'is preferably equal to the outer diameter of the ring 46 (FIG. 2A). Thesemiconductor element 44 includes a N /P silicon (Si) wafer Me, a thinmetallic upper layer 44b and a thin metallic lower layer 44c. The wafer44a can have a thickness of from 3 to 15 mils, for example. This waferMa can be, if desired, a N /P/P silicon wafer in accordance with thisinvention. The upper and lower layers 44b and Me can be of aluminum, andthe upper layer 44b provides an electrical ohmic contact from the N typesurface of wafer 44a to the lower surface of (an upper) ring 46 whilethe lower layer 44c provides an electrical ohmic contact from the P-typesurface of wafer 44a to the upper surface of (a lower) ring 46 and,incidentally, to the upper surface of (a lower) disc 42a. The upperlayer 44b is, of course, sufficiently thin (less than 2 microns thick,for example) to permit adequate penetration thereof by the betaradiation from the contiguous promethia layer 42b above it. in oneparticular embodiment, the upper layer 44!; is actually in the form of agrid (generally similar to a wire screen) wherein each mesh or enclosedspace allows free passage of the beta particles or radiationtherethrough. The upper and lower layers 44b and 460 can be of silver(Ag) instead of aluminum, and are preferably vapor deposited or platedon the wafer 454a. The lower layer 44c can be 1 mil thick although 2microns would be adequate.

The thin metallic layer and grid are both distributed or extendedelectrode forms which provide good ohmic contact with the full lower andupper surfaces of the semiconductor wafer 44a. A grid providing an ohmiccontact to a given semiconductor surface (unit reference) area has acertain fractional ohmic contact area and a remaining fractional openarea for passage of beta particles or other radiation. A thin metalliclayer obviously provides maximum (lowest resistance) contact over thefull semiconductor surface with, however, a zero fractional open areafor free passage of the beta particles or radiation. Of course, thedistributed ohmic contact area of a grid or any other such extendedelectrode form with a given semiconductor surface area must be adequateto achieve a suitable balance between the fractional open areaobtainable for free passage of the beta particles or radiationcommensurate with maintaining a sufficiently extensive and good (lowresistance) ohmic contact for the entire semiconductor surface area. Inthis respect, a minimum distributed ohmic contact area is required witha highly conductive (high carrier concentration) semiconductor surface.

in our invention, beta radiation is preferably coupled with either a NV?or N"/l /P silicon wafer. The N /P silicon wafer is a two-layer siliconsystem including a N -type layer characterized by a phosphorus (P)concentration of approximately to 10 atoms/cm. and a P-type layercharacterized by a boron (B) concentration of approximately 10 atoms/cm(or a P-type layer having a resistivity of approximately 1 ohm-cm). TheNHP/l silicon wafer can be produced from a N /P silicon wafer bydiffusing a suitable amount of boron into the lower surface of thelP-type layer or region of the silicon wafer to produce a P -type layertherein. The Nfi'P/P silicon wafer is a three-layer silicon systemincluding N -type and P-type layers as in the above N IP silicon wafer,and a P -type layer characterized by a boron concentration ofapproximately 10 to 10 atoms/cm? In both of these types of siliconwafers, arsenic (As), antimony (Sb) or bismuth (Bi) can be substitutedfor phosphorus, and aluminum, gallium (Ga), indium (in) or thallium (Tl)can be substituted for boron. Germanium (Ge), cadmium sulfide (CdS) andgallium arsenide (GaAs) semiconductors, among others, can be usedinstead of silicon. However, more power can be obtained from siliconcells than from the others. For example, roughly five times more powercan be usually derived from a silicon cell than from a generally similargermanium cell.

FIG. 3 is an enlarged fragmentary and central sectional view of adirectly fueled nuclear battery cell 62. A N /1P (or N*/P/Psemiconductor wafer 66 of silicon, for example, has both upper and lowersurfaces coated with thin metallic layers 66 and 68, respectively, whichcan be of aluminum, nickel or silver. Suitably deposited thereon arerespective layers 70 and 72 of a source of beta radiation material suchas promethia or promethium-l47 (Pm metal. The radioactive layers 70 and72 are smaller in diameter than that of the semiconductor wafer 64, asillustrated. The radioactive layers 70 and 72 are then fully covered byouter metallic layers 74 and 76, respectively, which can be of aluminumor silver and are for electrical contact.

The radially outer circumferential (lower) surface portion of the uppercover layer 74 contacts the corresponding portion of the thin metalliclayer 66 which is in contact with the surface of the P-type layer of thesemiconductor wafer 64. Similarly, the radially outer circumferential(upper) surface portion of the lower cover layer 76 contacts thecorresponding portion of the thin metallic layer 68 which is in contactwith the surface of the N -type layer of the wafer 64. Thus, the uppercover layer 74 is of positive polarity and the lower cover layer 76 isof negative polarity for the battery cell element 62. The cell elements62 can be readily stacked in series for a higher output voltage and, ofcourse, the stacks can also be suitably connected in parallel as may bedesired or required.

FIG. 4 is an, electron energy level diagram for a NVP/P semiconductorwafer 78. Nuclear-voltaic effects are initiated when radiation 80 entersthe semiconductor 78 and creates electron 82 and hole 84 pairs. A largenumber of these carriers (electrons and holes) diffuse to the vicinityof the abrupt (N P) junction 86 where the junction electric fieldaccelerates them to device terminals 88 and 90. By suitably adjustingthe device parameters, most of the carriers produced are collected undershort circuit conditions. The electrochemical potential or Fermi levelof the device under equibrium conditions is indicated by full line 92,and broken lines 94 and 96 represent the electrochemical potentials forelectrons and holes, respectively, resulting from electron and hole pairproduction of the device under radiation excitation. Brackets 98 shownnear the line 92 represent donor impurity atoms which have donated theirexcess valence electrons to the conduction band above the energy gap ofthe forbidden region. Similarly, brackets 100 shown near the line 92represent acceptor impurity atoms which have captured extra electronsfrom the valence band below the forbidden energy gap. It can also beseen that the P -type layer acts as a reflector of the free electrons.

Nuclear-voltaic energy conversion involves collecting electrons andholes at the terminals of an inhomogeneous semiconductor or metallicwafer. The electrons and holes result from electron-hole pair creationby the absorption of nuclear particles within the material. These chargecarriers are accelerated to the device terminals as a result of aninternal electric field which exists because of the inhomogeneous natureof the medium. Electrons and holes live longer in semiconductors than inmetals. Thus, the most practical approach tonuclear-voltaic energyconverters involves the use of a semiconductive material for at leastpart of the system. For example, a two-electrode system can contain onelayer of semiconduetive material and another layer characterized as (1)-the same kind of semiconducting material but with a differentelecl060ll 0592 trochemical potential as can be obtained by doping thelayer differently than the first layer, (2) a different kind ofsemiconductor, or (3) a metal. The first approach is, of course,followed in accomplishing this invention.

Radiation employed in the various embodiments of this invention ispreferably beta nuclear particles supplied by a source of promethia orpromethium-I47 metal. A flux of approximately 5 10 betas/cm /sec can beobtained from a layer of promethia of about 0.001 cm thickness andapproximately l betas/cmls ec in the case of a layer of promethium-147metal of about the same thickness. The energy spectrum of beta particlesemitted from a radioactive promethium source (the metal or its oxide) issuch that very little radiation damage is caused in siliconsemiconductors. The thickness of the semiconductor wafer is selected sothat most of the radiation is absorbed by the semiconducting medium.Where promethium-l47 metal or its oxide is used in conjunction with a N/P or NVPIP silicon semiconductor wafer, the thickness of the wafer needonly be a'pproximately0.0l cm, for example.

Beta sources other than promethium include the isotopes of tritium (Hnickel-63 (Ni and strontium-90 andyttrium-90 (Sr-Y). Such other betasources as these, however, are used in this invention largely forspecial applications. More power can be obtained from promethium-147metal or its oxidethan with H and Ni? For example, tritium may bepreferred under certain circumstances because of its longer half-life.Similarly, the available energy in strontium-90 and yttrium-90 sourcesgreatly exceeds that of Pm sources, and this is useful for certainapplications even though such high energy beta particles would causegreater radiation damage in the semiconductor than the lower energy betaparticles emitted from the other sources.

Beta particles emitted by a promethium source have a maximum energy ofapproximately 0.230 million electron volts (mev), approximately 0.0186mev from tritium, and approximately 0.54 and, 2.26 mev from strontium-90and yttrium-90 (Sr" and Y are in secular equilibrium and cannot beseparated due to the short half-life of Y as is well known). Radiationdamage in P-type silicon starts at about 0.20 mev so that a promethiumsource coupled with a silicon N /P or N ll /P cell is almost ideal andprovides optimum power output. Germanium has a higher threshold level(of about 0.4 mev) for the start of radiation damage than silicon butthe power obtainable from silicon is about five times better. Othernuclear particles or radiation such as alpha, neutrons or gamma can beused besides beta in this invention. However, use of such otherparticles or radiation is limited to other specific purposes and is notparticularly practical for the purpose of a nuclear battery. Forexample, the most energetic alpha particles from radionuclides lose alltheir energy within several microns in silicon or other semiconductingmaterials.

FIG. is a circuit diagram showing a resistive load R connected topositive and negative terminals 102 and 10A of a NH? (or N /P/Psemiconductor wafer 106. The terminals 102 and 104 connect respectivelywith thin metallic coatings on the faces of the wafer 106. The thin, lowresistance, metallic coatings are only needed to cover large area faces,of course. An ammeter 108 is connected in series with the load R and avoltmeter 110 is connected across the terminals 102 and 104. The wafer106 is operatively associated with fuel element 112 which is aradioactive source providing a nuclear particle flux 114 (of betaradiation) to the wafer. The fuel element 112 is, of course, normallypositioned substantially against the wafer 106 to form a battery cell116. A current I will flow through the load R and can be measured by theammeter 108. Similarly, the voltage V across the load R can be measuredby the voltmeter 110.

FIG. 6 is a circuit diagram showing an equivalent circuit for the singlecell 116 (FIG. 5) having its terminals 102 and 104 connected across theresistive load R The voltage-currentcharacteristics of the cell 116 arewell described by the following relationship:

I= I, (V/R I, [exp (V-RJ/AkT) -l] [Eq. I]

where I Current through resistive load R V= Voltage across R R,= Seriesresistance of nuclear-voltaic cell resulting from imperfect terminalcontacts to'cell surfaces R, Effective shunt resistance of cell I,Reverse current of semiconductor wafer A Parameter characterizing N Pjunction 1, Generation current k Boltzmann's constant T= Absolutetemperature The diode d in FIG. 6 represents the N P junction, and theseries contact resistance R, is usually negligible and it can behenceforth considered that R, 0. In that case, the short circuit currentI (I measured when V 0) is equal to 1,. On a per-unit-area basis, thecurrent density of a single cell is given by the following equation:

J=J,,, -J,, [exp (V/AkT) l 1 G,,,.V [Eq. 21 where I, =1,

J Current (I) per unit area of single cell J, Short circuit current(I,,,) per unit area of single cell G Effective shunt conductance perunit area of single cell 1/(R area)] The open circuit voltage V of asingle cell is given by the following equation:

V, AkT- log [1,, J G, V /Jfl [Eq. 3] The reverse current density .I canbe appropriately denoted as a leakage current parameter and the propervalue of J to use when describing betavoltaic results is that valueobtained when the N? junction is subjected to a forward bias voltage ofabout 0.0 to 0.4 volt. When reverse bias conditions are used todetermine .I.,, an improper result is generally obtained.

The short circuit current is determined primarily by the diffusionlength (which is related to lifetime) of the minority carriers and thegeneration rate of those carriers. The latter depends on how efiectivelybeta particles are absorbed in the semiconducting medium and upon theaverage energy of the beta particles. The generation rate is directlyproportional to the beta particle average energy; however, radiationdamage effects to the semiconductor must also be considered in selectinga. suitable beta source. The parameters I, and

A are tightly coupled, and these parameters reflect the quality of thesemiconductor element or device. In the case of an ideal silicon NPjunction, .1 is about 10' amp/cm and A 1.0. In real devices, however,defects on the surface and near the junction change these valuesconsiderably. For example, in the voltage range of interest, typicalcommercial silicon solar cells are characterized by values of .1 of theorder of 10' amp/cm and A of approximately 2.5.

The net effect of the change in values from the ideal case is that V ofthe device is considerably lowered, and the maximum power is alsolowered. The existence of defects in the junction region causeselectron-hole recombination currents or leakage currentsthat subtractfrom the available output current. Surface defects also account forlosses, but the junction recombination currents are the primary reasonfor solar cells not behaving as ideal cells under low bias voltageconditions. The parameter G, takes into account current shunting pathswhich are, of course, sources of loss in a betavoltaic energy converter.The paths can arise from inhomogeneities in the planar junction, ordefective re gions near the edge of the device. Commercial silicon solarcells have values of G of about 10' ohm cm'. Thus, if the effective areaof such a cell is 1 cm the shunt resistance, R 1/(G,,, area), would beabout 10 ohms.

FIG. 7 is a graph illustrating the J-V and Pw-V characteristics of asingle cell constructed according to our invention. The cell had aplanar junction area of 2.85 cm and was fueled with a promethium-147radioisotope, by utilizing a promethia source having an area of 2.3 8 cmand a layer thickness of approximately 5.3 mg/crn. Promethia activitywas approximately 678 curies/gm such that a total source strength of1288 microwatts/cm was available. Such cells or devices are much moresuited to betavoltaic energy conversion than the solar cells mentionedabove. Devices of the nature as that having the typical betavoltaic dataof FIG. 7 are characterized by the following parameters: 1 amplcm A LSand G,,, (0.5 10") ohm cm'. With the promethium-147 radioisotope fuel,the energy spectrum of beta particles emitted therefrom is such thatvery little radiation damage occurs in silicon devices.

The J-V characteristic of the single cell fueled with promethium-147 isshown at the beginning of life by a full line 118 in FIG. 7, and isshown by broken lines 120, 122 and 124 after 1, 2 and 3 years,respectively. The beginning of life output power density (Pw) availablefrom a single cell (output power per unit area of its active area) isshown by a full line 126. The short circuit current density .1 generallydecays as does the promethium-147 radioisotope (of 2.6 years half-life).Further, the single cell open circuit voltage V decays as follows:

FIGS. 8A, 8B, 8C and 8D are graphs which were plotted from experimentalresults and show typical characteristics of a promethia-fueled, silicon,betavoltaic single cell as a function of promethia layer thickness. Thecell included a N"'/P/P silicon wafer with a resistivity p 5 0.3 ohm-cm,A 1.5, .1 8.8 10' amp/cm and the promethia activity was 678 cuties/gm.In FIG. 8A, the short circuit current density J, (microarnpslcm isplotted as a function of promethia layer thickness (milligramslcmSimilarly, in FIGS. 8B, 8C and 8D, the open circuit output voltage V(volts), the maximum output power density Pw (microwatts/cm) and deviceor cell efficiency are respectively plotted as a function of promethialayer thickness (mglcm This data is used to determine the optimum layerthickness promethia source for a given application. For example, ifdevice efficiency is the dominating factor in any consideration, it isapparent from FIG. 8D that promethia sources having a layer thickness ofabout 1 or 2 mg/cm should be used; however, where power output is thedominating factor, it can be seen from FIG. 8C that promethia sourceshaving a layer thickness of the order of 10 mg/cm should be used.

FIGS. 9A and 9B are respectively a perspective view of a bi-directionalfuel element or source 128, and a fragmentary and enlarged sectionalview thereof. The fuel element 128 is preferably a thin disc 130 asshown in FIG. 9A, and emits nuclear particles in two directions asindicated by arrows 132. Radioisotopic fuel material is, for example,held and supported in a suitable matrix. In this instance, small grains134 of promethia are used to form a disc and then these grains arethinly coated with approximately 1 micron of metal 136 to hold themtogether as indicated in FIG. 9B. The metal 136 is preferably aluminum;however, nickel, copper (Cu) or tantalum can also be satisfactorilyused. The metal 136 can be deposited on the grains 134 by vapordeposition or sputtering. The disc 130 can alternatively be made ofpromethium-l47metal. However, such a metal disc cannot be much greaterthan 10 microns in thickness if the device efficiencies of the improvedlater models are to be maintained. It appears that promethium-147 metalcannot presently be rolledout much thinner than 50 to 75 microns, anddirect depositing of the metal is required.

FIGS. 10A and 10B are exploded perspective views of a two-cellbetavoltaic energy converter 138 using the bi-directional source 128(FIG. 9A), wherein the cells are connected respectively in parallel andin series. A cell is, of course, a unit including a fuel element orsource and an associated N /P or N /P/P semiconductor element or wafer.The source and wafer are preferably promethium (metal or its oxide) andsilicon, respectively. Thus, the bi-directional source 128 in FIGS. 10Aand 10B is a mutual source for the wafers 140 and 142. The source 128 isnormally positioned contiguously to the N -type layers 140a and 142a ofthe wafers 140 and 142. As shown in FIG. 10A, the P- type layers 140band 142b (with thin metallic coatings thereon) are both connected topositive terminal 144, and the N -type layers 1470a and 142a (with thinmetallic coatings or grids thereon) are both connected to negativeterminal 146. In FIG. 108, however, the P- type layer 1421: is connectedto positive terminal 148,

the N -type layer 142a is connected to the P-type layer 1401; and the N-type layer 1411a is connected to negative terminal 151).

FIG. 11 is an elevational view of an NW1 (or NflP/P semiconductor wafer152 having a coating 3 of promethium-l47 metal or promethia depositeddirectly onto the N -type layer 156 of the wafer 152. The promethiumcoating 154 can be deposited directly onto the surface of the N typelayer 156 either by vapor deposition, sputtering or electroplatingtechniques. Negative electrode strip 158 is bonded to the N -type layer156 at its peripheral margin (which has a thin metallic coatingthereon), and positive electrode strip 161) is bonded to the (thinlymetal coated) P-type (or P -type) layer 162 at its peripheral margin asillustrated. The surface of the N' -type layer 156 provides directsupport for the promethium coating 154, and an intervening conductivemetal coating or grid is not used. The advantages include greatersimplicity of construction and significantly increased efficiency.

FIG. 12 is an exploded perspective view of a two-cell betavoltaic energyconverter 164 having a radioactive material coated on at least onesemiconductor wafer. The converter 164 includes N /P of an enclosingpair, (or N /P/P semiconductor wafers 166 and 168. The N -type layer168a of the wafer 168 has a coating 170 thereon of promethium-147 metalor promethia, for example, just as the wafer 152 (FIG. 11). The wafer166 need not have a radioactive coating thereon and is normallypositioned with its N -type layer 166a contiguous to the coating 171) totake advantage of its emitted nuclear particles. Of course, the N -typelayer 166a can have a coating thereon similar to the coating 170. Inthis instance, each of such coatings can be formed with a significantlylower layer thickness. The two cells of the converter 164 are shownconnected in parallel to the positive and negative terminals 172 and174; however, it should be clear that the cells can be readily connectedin series to the terminals 172 and 174. Of course, the faces of theP-type (or P -type) layers 16617 and 168b have thin metallic coatingsthereon, and the marginal ring areas of the N -type layers 166a and 168aalso have such coatings thereon.

FIG. 13 is an exploded perspective view of a highly compact andpractical form of a nuclear battery 176. Most applications requireseveral cells in a nuclear battery. The voltage requirements determinethe number of cells to be connected in series, while the currentrequirements determine the cell areas and/or the number of cells to beconnected in parallel. The final design, therefore, includes one or morecells combined in a series and/or parallel network to meet requiredspecifications. For example, the nuclear battery 30 embodiment shown inFIG. 1 is a series connection of cells, and certain models (DL-lOA-2 andDL-IOOA 1) thereof meet the following specifications.

Model Diameter of cylindrical envelope, D (cm) l.l 8 1.55 Deviceefficiency 1.04 0.84

The planar, multiple section, cell embodiment of the nuclear battery 176can meet the above specifications than that of the battery 30. Thebattery 176 includes a fuel element 178 and a multiple section N IPIPsemiconductor element 180. The fuel element 171%.

comprises a disc 182 and a thin coating 1841 of radioactive materialthereon. The disc 182 is madeof aluminum and the coating 184 is ofpromethia, for example. Thesemiconductor element can be made by firstdiffusing phosphorus into the upper surface active areas of a P-typesilicon wafer 186 using a suitable mask (not shown) to produce a N -typelayer 188 thereon. Boron is then similarly diffused into the lowersurface active areas of the wafer 186 to produce a P*- type layer 190thereon. The wafer 186 is next cut into appropriate sectors 192 whichare suitably cemented back together in disc form to an electricallyinsulating cross 192a made of material such as ceramic. In oneconstruction, the sectors 192 were cemented directly on the surface of aceramic substrate plate so that the cross 192a was of air. The sectors192 were connected in series by (three) leads 194 which connect a N-type layer 188 of onesector to the P -type layer 190 of a succeedingsector in a clockwise direction. Positive output lead 196 is connectedto the P -type layer of the first (upper left) sector, and negativeoutput lead 198 is connected to the N -type layer of the last (lowerleft) sector of the semiconductor element 180. As in the other versionsof this invention, the surfaces of the N*- type and P -type layers 188and 190 of each sector 192 have a thin metallic coating providedthereon.

FIG. 14 is a graph of the current (I) and power (Pwr) versus voltage (V)characteristics of a planar, four section cell, nuclear batteryembodiment similar to that shown in FIG. 13. The semiconductor elementwas coupled to a promethia fuel element or source wherein the fuel disc,is coated with. promethia at a layer thickness of approximately 8mg/crn and having an activity of about 660 curies/gm. It can be notedthat maximum power occurs at a relatively high voltage, for a singlecell configuration.

FIG. 15 is anexploded perspective view of a planar, multiple section,cell embodiment of a nuclear battery 269 which is superior from afabrication point of view than the battery 176 of FIG. 13. The battery201) includes fuel element 202 and a multiple section N llllsemiconductor element 204;. In this configuration, P- type (silicon)wafer 206 need not be cut into sectors since P' -type layers 208 and N-type layer 216 are formed by deep diffusion or ion implantation (ionbeam directed into material) techniques in the wafer as axial guard andisolating walls, respectively, and completely separate and isolate eachcell section. The P -type wall layers 208 are located between the planarN -type layers 210a and the N -type wall layer 2111. The wall layer 210can be ceramic but this would require cutting of the wafer 206. The cellsections can be connected in series by (three) leads 212, and positiveand negative output leads 21 1 and 216 are connected to the first andlast sections as illustrated. The

l060ll 0595 exposed surfaces of the guard layers 20% and of the planarlayers Elba are, of course, plated with a thin metallic low resistancecoating. it may be noted that a single cell including a promethia sourceand a silicon N"? or NVP/Pf wafer, and which utilizes only one activearea or section, supplies electrical power characteristically atvoltages of about 0.3 volt. Thus, multiple section cell embodiments ofnuclear batteries are highly desirable to obtain much higher outputvoltages from a relatively compact device.

FIG. 16 is a partially fragmentary and exploded perspective view of alaminar, multiple section, cell configuration of a nuclear battery 218.The battery 218 in cludes a fuel element 220 and a multiple sectionNVP/l semiconductorelement 222. The illustrated structure is believed tobe self-explanatory in view of the preceding description on multiplesection cell embodiments. The laminar, multiple section battery 218 mayat first sight appear to be equivalent to the planar devices of FIGS. i3and 15. It is not, however. The nuclear particle flux 224 is parallel tothe main N P junctions in this embodiment. The silicon semiconductorelement 222 preferably has, for example, a height h greater thanapproximately 1 microns and a width w of the order of 1 cm. Thesedimensions can be varied by using another fuel element similar to thefuel element 22f) on the opposite (lower) side of the semiconductorelement 222, and also on the front and rear sides thereof. One of theadvantages of this battery (218) configuration is that very high voltagedevices can be easily made by having any desired number of lateral cellsections. The lateral end surfaces have, of course, metallic coatingsdeposited thereon to which are soldered the positive and negativeelectrode strips 226 and 228.

FlG. K7 is an electron energy level diagram for about two sections ofthe NVP/P semiconductor element 222 shown in H6. 16. its operation underexposure to radiation is indicated in the diagram. It can be seen fromthe diagram that the main junctions are those between the N -type and P-type layers. Current flows from the electrode strip 226 (FIG. 16)attached to the coated left end W-type layer and to the electrode strip228 attached to the coated right end N -type layer when a load isconnected between the electrode strips.

P16. 118 is an exploded and partly fragmentary perspective view of aneedle-like or elongated cylindrical, multiple section, cell embodimentof a nuclear battery 236. The battery 230 is fabricated in a mannergenerally similar to that of the planar battery 176 of H6. 13. Thebattery 23% includes a fuel element 232 and a multiple section N IP (orNVP/P") semiconductor element 234. in this instance, however, the fuelelement 232 comprises a thin cylindrical shell 232a of, for example,aluminum foil having a promethia layer 23% deposited on its innersurface. The semiconductor element 23d is fabricated by difiusingphosphorus circumferentially into a P-type cylinder of semiconductormaterial. The cylinder is then cut into uniform sections 236 having aP-type core 236a and a surrounding N*- type outer layer 23617. Thenormally upper surface of the P-type core 236a is covered with ametallic coating or sheet 238 which can be aluminum, and thecircumferential surface of the N -type layer 236i: is covered with ametallic grid or thin metallic coating 2% which can also be of aluminum.The periphery of the coating or sheet 23% covering the normally uppersurface of the P-type core 236a is, of course, spaced from the N?junction so that there is no interaction therewith. For a N /P/Psemiconductor, the coating 238 would be deposited on top of a central P-type cylinder formed axially in the P-type core 236a.

The sections 236 are separated by insulator discs 242 which arepreferably made of ceramic. Each disc 242 has a hole 242a through whichpasses a lead 244 connecting a P-type core 236a of one section 236 tothe N -type layer 236b of an adjacent upper section. The sections 236are thus connected in series with a positive output lead 246 and anegative output lead 248. The insulator discs 242 can be cemented orsuitably secured to adjacent sections 236, and then inserted andpositioned in the cylindrical fuel element 232 shell. While acylindrical junction surface is utilized in obtaining the elongatedcylindrical battery 230, it is apparent that other configurations ofnuclear batteries can be obtained so'long as a suitable junction'can beformed therein.

It is to be understood that the exemplary embodiments of this inventionare merely illustrative of, and not restrictive on, our broad inventionand that various changes in design, structure and arrangement may bemade therein without departing from the true spirit and scope of theinvention.

We claim:

1. In a nuclear battery, a cell comprising:

a fuel element including a radioactive source of nuclear particleshaving a known maximum energy, said radioactive source comprising asource of beta particles; and

a semiconductor element positioned in at least close proximity to saidfuel element and irradiated by the same, said semiconductor elementincluding a semiconductor wafer and relatively thin, electricallyconductive, distributed ohmic contact members provided on respectivefaces of said wafer, and said wafer comprising a system of at least ahigh carrier concentration first-type layer and a lower carrierconcentration second-type layer of semiconductor material havingrespectively different electrochemical potentials and having an energythreshold level of radiation damage compatible with, and at least of thesame order as, the maximum energy of said nuclear particles, said layershaving a junction therebetween and said fuel element being positionedoperatively close to said junction adjacent to said high carrierconcentration first-type layer, at least said ohmic contact memberadjacent to said fuel element providing a relatively large fractionalopen area for passage therethrough of said nuclear particles whereby along life cell of maximum output voltage and high power output isobtained.

2. The invention as defined in claim 1 wherein said fuel elementincludes a unitary radioactive source member, and said wafer systemfurther comprises a high carrier concentration layer of said second-typeelectrochemical potential material, said latter layer serving primarilyas a reflector barrier whereby a long life cell of maximum outputvoltage and high power output is obtained.

3. The invention as defined in claim 2 wherein said source memberincludes a backing disc having a layer of radioactive material providedon a surface thereof and which is a promethium source of beta particles,

and said system includes a silicon system of Ni-type, P-

type and P -type layers of different electrochemical potential materialand having carrier concentrations of the order of approximately 10 and10 atoms/cm, respectively, said N -type and P-type layers having saidjunction therebetween, said P -type layer serving primarily as saidreflector barrier and said fuel element being positioned operativelyclose to said junction adjacent to said N*-type layer.

4. The invention as defined in claim ll wherein said fuel elementincludes a bi-directional source which is a unitary radioactive discmember comprising promethia and a matrix to hold and support saidpromethia, and said semiconductor element is positioned in at leastclose proximity to one side of said bi-directional source, and furthercomprising another similar semiconductor element positionedsymmetrically to the other side of said bi-directional source.

5. The invention as defined in claim 2 wherein said fuel element is of aplanar form, and said semiconductorelement is of a correspondinglysimilar planar form and having multiple sections which are insulatedfrom each other and operatively connected in at least a partially seriesarrangement to provide an output voltage higher than that available froma commensurate cell having a unitary semiconductor element.

.6. The invention as defined in claim 2 wherein said fuel element is ofa planar form, and said semiconductor element is of a laminar formhaving laterally disposed multiple sections with planes orientedperpendicularly to the plane of said fuel element, said sections beingoperatively coupled in series to provide an output voltage higher thanthat available from a commensurate cell having a unitary semiconductorelement.

7. The invention as defined in claim 1 wherein said fuel element is ofan elongated and hollow cylindrical form, and said semiconductor elementis of a correspondingly elongated and solid cylindrical form positionedconcentrically within said fuel element and having axially disposedmultiple sections which are insulated from each other and operativelyconnected in at least a partially series arrangement to provide anoutput voltage higher than that available from a commensurate cellhaving a unitary semiconductor element.

8. The invention as defined in claim ll wherein said fuel elementincludes a unitary radioactive source member comprising a backing dischaving a layer of radio-active material provided on a surface thereofand which is a promethium source of beta particles, and said systemincludes a silicon system of N type and P- type layers of differentelectrochemical potential material and having carrier concentrations ofthe order of approximately 10 and 10 atoms/cm, respectivea fuel elementcomprising a radioactive source of nuclear particles having a knownmaximum energy, said fuel element including a unitary radioactive sourcemember, and

a semiconductor element positioned in at least close proximity to saidfuel element and, irradiated by the' same, said semiconductorelementcomprising a semiconductor wafer and relatively thin, I electricallyconductive, dis- I tributed ohmic contact members provided on respectivefaces of said wafer, and said wafer in cluding a system of atleast ahigh carrier concentration first-type layer and a lower carrierconcentration second-type layer'of semiconductor material havingrespectively different electrochemical potentials and having an energythreshold level of 'radiationdamage compatible with, and at least of thesame order as, the maximum 'energy of said nuclear particles, saidlayers having a junction therebetween and said fuel element beingpositioned operatively close to said junction adjacent to said highcarrier concentration first-type layer;

a'plurality of electrically conductive ring members corresponding innumber to said cells and positioned concentrically about said fuelelements, respectively;

electrically conductive end members sandwiching said cells of saidstack, said ring members axially contacting said end members and saidohmic contact members of said wafers and providing a series connectionfrom one of said end members through said semiconductor elements of saidcells to the other of said end members;

spring means for biasing and maintaining said end members and cells ofsaid stack in effective series contact throughout the same; and

a pair of electrode terminals adapted to be connected respectively tosaid end members, whereby a long life battery of maximum output voltageand high power output is obtained.

10. A nuclear battery comprising: a fuel element including a radioactivesource of nuclear particles having a known maximum energy, said fuelelement being of a planar form; and

a semiconductor element positioned in at least close proximity to saidfuel element and irradiated by the same, said semiconductor elementbeing of a correspondingly similar planar form to said fuel element andincluding multiple sections which are insulated from each other andelectrical leads operatively connecting said sections in at least apartially series arrangement to-provide a higher output voltagetherefrom, each of said sections comprising a semiconductor wafer andrelatively thin, electrically conductive, distributed ohmic contactmembers provided on respective faces of said wafer and connecting withsaid leads, and said wafer including a system of at least a high carrierconcentration first-type layer and a lower carrier concentrationsecond-type layer of semiconductor material having respectivelydifferent electrochemical potentials and having an energy thresholdlevel of radiation damage compatible with, and at least of the sameorder as, the maxl060ll 0597 imum energy of said nuclear particles, saidlayers having a junction therebetween and said fuel element beingpositioned operatively close to said junction adjacent to said highcarrier concentration first-type layer whereby a long life battery ofmaximum output voltage and high power output is obtained.

11. The invention as defined in claim 9 wherein said source memberincludes a backing disc having a layer of radioactive material providedon a surface thereof and which is a promethium source of beta particles,at least said ohmic contact member adjacent to said fuel elementprovides a relatively large fractional open area for free passagetherethrough of said nuclear particles, said system includes a siliconsystem of at least N -type and P-type layers of differentelectrochemical potential material and having carrier concentrations ofthe order of approximately 10 and 10 atoms/cm, respectively, said N-type and P-type layers having said junction therebetween and said fuelelement being positioned operatively close to said junction adjacent tosaid N*- type layer, and said spring means includes an electricallyconductive spring ring for axially biasing uniformly over a wide baseagainst one of said end members of said stack, and further comprising ashielding container for containing and primarily providing radiationprotection containment of said stack, and a fire container forcontaining said shielding container and primarily providing hightemperature protection containment of said stack, one of said electrodeterminals being mounted on and insulated from said fire container andsaid spring ring electrically connecting the one of said end members tosaid shielding container which is in electrical contact with said firecontainer sewing as the other of said electrode terminals.

12. The invention as defined in claim 10 wherein said fuel elementincludes a unitary radioactive source member which is a promethiumsource of beta particles, at least said ohmic contact member adjacent tosaid fuel element provides a relatively large fractional open area forfree passage therethrough of said nuclear particles, and said systemincludes a silicon system of at least N -type and P-type layers ofdifferent electrochemical potential material and having carrierconcentrations of the order of approximately 10 and 10 atoms/cm,respectively, said N -type and P-type layers having said junctiontherebetween and said fuel element being positioned operatively close tosaid junction adjacent to said N -type layer.

2. The invention as defined in claim 1 wherein said fuel elementincludes a unitary radioactive source member, and said wafer systemfurther comprises a high carrier concentration layer of said second-typeelectrochemical potential material, said latter layer serving primarilyas a reflector barrier whereby a long life cell of maximum outputvoltage and high power output is obtained.
 3. The invention as definedin claim 2 wherein said source member includes a backing disc having alayer of radioactive material provided on a surface thereof and which isa promethium source of beta particles, and said system includes asilicon system of N -type, P-type and P -type layers of differentelectrochemical potential material and having carrier concentrations ofthe order of approximately 1019, 1016 and 1019 atoMs/cm3, respectively,said N -type and P-type layers having said junction therebetween, said P-type layer serving primarily as said reflector barrier and said fuelelement being positioned operatively close to said junction adjacent tosaid N -type layer.
 4. The invention as defined in claim 1 wherein saidfuel element includes a bi-directional source which is a unitaryradioactive disc member comprising promethia and a matrix to hold andsupport said promethia, and said semiconductor element is positioned inat least close proximity to one side of said bi-directional source, andfurther comprising another similar semiconductor element positionedsymmetrically to the other side of said bi-directional source.
 5. Theinvention as defined in claim 2 wherein said fuel element is of a planarform, and said semiconductor element is of a correspondingly similarplanar form and having multiple sections which are insulated from eachother and operatively connected in at least a partially seriesarrangement to provide an output voltage higher than that available froma commensurate cell having a unitary semiconductor element.
 6. Theinvention as defined in claim 2 wherein said fuel element is of a planarform, and said semiconductor element is of a laminar form havinglaterally disposed multiple sections with planes orientedperpendicularly to the plane of said fuel element, said sections beingoperatively coupled in series to provide an output voltage higher thanthat available from a commensurate cell having a unitary semiconductorelement.
 7. The invention as defined in claim 1 wherein said fuelelement is of an elongated and hollow cylindrical form, and saidsemiconductor element is of a correspondingly elongated and solidcylindrical form positioned concentrically within said fuel element andhaving axially disposed multiple sections which are insulated from eachother and operatively connected in at least a partially seriesarrangement to provide an output voltage higher than that available froma commensurate cell having a unitary semiconductor element.
 8. Theinvention as defined in claim 1 wherein said fuel element includes aunitary radioactive source member comprising a backing disc having alayer of radio-active material provided on a surface thereof and whichis a promethium source of beta particles, and said system includes asilicon system of N -type and P-type layers of different electrochemicalpotential material and having carrier concentrations of the order ofapproximately 1019 and 1016 atoms/cm3, respectively, said N -type andP-type layers having said junction therebetween and said fuel elementbeing positioned operatively close to said junction adjacent to said N-type layer.
 9. A nuclear battery comprising: a plurality of cellsarranged in a series stack, each of said cells including a fuel elementcomprising a radioactive source of nuclear particles having a knownmaximum energy, said fuel element including a unitary radioactive sourcemember, and a semiconductor element positioned in at least closeproximity to said fuel element and irradiated by the same, saidsemiconductor element comprising a semiconductor wafer and relativelythin, electrically conductive, distributed ohmic contact membersprovided on respective faces of said wafer, and said wafer including asystem of at least a high carrier concentration first-type layer and alower carrier concentration second-type layer of semiconductor materialhaving respectively different electrochemical potentials and having anenergy threshold level of radiation damage compatible with, and at leastof the same order as, the maximum energy of said nuclear particles, saidlayers having a junction therebetween and said fuel element beingpositioned operatively close to said junction adjacent to said highcarrier concentration first-type layer; a plurality of electricallyconductive ring members corresponDing in number to said cells andpositioned concentrically about said fuel elements, respectively;electrically conductive end members sandwiching said cells of saidstack, said ring members axially contacting said end members and saidohmic contact members of said wafers and providing a series connectionfrom one of said end members through said semiconductor elements of saidcells to the other of said end members; spring means for biasing andmaintaining said end members and cells of said stack in effective seriescontact throughout the same; and a pair of electrode terminals adaptedto be connected respectively to said end members, whereby a long lifebattery of maximum output voltage and high power output is obtained. 10.A nuclear battery comprising: a fuel element including a radioactivesource of nuclear particles having a known maximum energy, said fuelelement being of a planar form; and a semiconductor element positionedin at least close proximity to said fuel element and irradiated by thesame, said semiconductor element being of a correspondingly similarplanar form to said fuel element and including multiple sections whichare insulated from each other and electrical leads operativelyconnecting said sections in at least a partially series arrangement toprovide a higher output voltage therefrom, each of said sectionscomprising a semiconductor wafer and relatively thin, electricallyconductive, distributed ohmic contact members provided on respectivefaces of said wafer and connecting with said leads, and said waferincluding a system of at least a high carrier concentration first-typelayer and a lower carrier concentration second-type layer ofsemiconductor material having respectively different electrochemicalpotentials and having an energy threshold level of radiation damagecompatible with, and at least of the same order as, the maximum energyof said nuclear particles, said layers having a junction therebetweenand said fuel element being positioned operatively close to saidjunction adjacent to said high carrier concentration first-type layerwhereby a long life battery of maximum output voltage and high poweroutput is obtained.
 11. The invention as defined in claim 9 wherein saidsource member includes a backing disc having a layer of radioactivematerial provided on a surface thereof and which is a promethium sourceof beta particles, at least said ohmic contact member adjacent to saidfuel element provides a relatively large fractional open area for freepassage therethrough of said nuclear particles, said system includes asilicon system of at least N -type and P-type layers of differentelectrochemical potential material and having carrier concentrations ofthe order of approximately 1019 and 1016 atoms/cm3, respectively, said N-type and P-type layers having said junction therebetween and said fuelelement being positioned operatively close to said junction adjacent tosaid N -type layer, and said spring means includes an electricallyconductive spring ring for axially biasing uniformly over a wide baseagainst one of said end members of said stack, and further comprising ashielding container for containing and primarily providing radiationprotection containment of said stack, and a fire container forcontaining said shielding container and primarily providing hightemperature protection containment of said stack, one of said electrodeterminals being mounted on and insulated from said fire container andsaid spring ring electrically connecting the one of said end members tosaid shielding container which is in electrical contact with said firecontainer serving as the other of said electrode terminals.
 12. Theinvention as defined in claim 10 wherein said fuel element includes aunitary radioactive source member which is a promethium source of betaparticles, at least said ohmic contact member adjacent to said fuelelement provides a relatively large fractioNal open area for freepassage therethrough of said nuclear particles, and said system includesa silicon system of at least N -type and P-type layers of differentelectrochemical potential material and having carrier concentrations ofthe order of approximately 1019 and 1016 atoms/cm3, respectively, said N-type and P-type layers having said junction therebetween and said fuelelement being positioned operatively close to said junction adjacent tosaid N -type layer.